Demands for carbon fibers in general industrial uses related to construction, civil engineering and energy are increasing year by year. In order to obtain the required fineness of carbon fibers in methods for forming a large structural material, for example, weaving and filament winding methods, at present, a certain number of carbon fiber bundles with about 7,000 to 20,000 deniers are lined up to perform forming. However, in forming by lining up, there is a problem wherein gaps are opened between lining up units to produce an irregular impregnation of the resin.
Furthermore, if carbon fiber bundles with about 7,000 to 20,000 deniers are used, especially, when a large and thick formed body is produced, the laminating number and the winding number must be increased, and it is disadvantageous in the aspect of forming time. Specifically, if the package of carbon fibers having a large number of filaments and a large thickness is available, there is advantage wherein the laminating number and the decrease of the winding number of carbon fibers to a high-dimensional processing facility, the shortening of forming time, and making the creel facility compact are feasible.
Patent Document 1 proposes a carbon fiber package of a square-end type obtained by winding carbon fibers having a fineness of 25,000 deniers or higher on a bobbin, wherein the width per unit fineness of the carbon fibers is in the range of 0.15×10−3 to 0.35×10−3 mm/denier, the traverse angle in the beginning and the end of winding are in the range of 10 to 30° and 3 to 15°, respectively, and the fractional portion W0 of the winding ratio W is in the range of 0.12 to 0.88.
Patent Document 1: Japanese Patent Application Laid-Open No. 10-316311